How to convert the cube (or any object) into a static mesh asset

Summon a cube 
 Select the cube you have summoned in the game world. 
 In the Details panel, go to the "Mesh" section and click on the arrow next to the mesh asset name. 
 Select "Create Static Mesh" from the dropdown menu. This will create a new static mesh asset that represents your cube. 
 u can now use this to create special objects